The proposed K01 Award will provide the candidate, Dr. Kreniske, with the skills to achieve his long-term goal of being an independent HIV investigator and an international leader who leverages digital technology to improve adolescent and young adult (AYA) uptake of HIV prevention (including PrEP and HIV testing) and linkage to behavioral health care. The candidate is a developmental psychologist with experience in qualitative and cross- sectional research, domestically and internationally. The proposed training and research experience will expand the candidate?s ability to design and evaluate interventions for AYA at high risk for HIV infection and address the high priority topic of the National Institute of Health (NIH) Office of AIDS Research (OAR) of reducing the incidence of HIV. To achieve his overall goals, Dr. Kreniske will receive additional training in: (1) longitudinal data analysis for the purposes of interpreting associations between mobile phone use and protective and risk factors for HIV infection in under-resourced settings; (2) adapting mobile phone-based interventions to address multiple HIV risk factors as they relate to HIV prevention and the HIV care cascade; (3) evaluating mobile phone- based interventions for AYA in under-resourced settings using randomized controlled trials (RCT); and (4) professional skills for a successful independent research career, including grant and manuscript writing. The candidate has assembled a mentorship team of national and international leaders who will support his successful transition to independence through coursework, directed readings, one-on-one meetings, hands-on research activities, and completion of an independent research project. Dr. Kreniske?s work is based in East and Southern Africa (ESA) where AYA have the highest rates of HIV infection worldwide. Mental health and substance use affect decision making about sexual and reproductive health and thus function as critical barriers to prevention of HIV infection. AYA, particularly in this socio-cultural context, face unique challenges in accessing counselors who can provide mental health and substance use assessment and treatment. To address these challenges the candidate will identify how technology is related to known HIV risk factors (e.g. sexual behaviors, mental health symptoms, substance use) and adapt and evaluate a mobile phone-based intervention. This will serve as proof of concept for an R01 proposal to evaluate a scalable mobile phone-based intervention to reduce HIV infection by targeting at risk AYA. Research and training will occur at NYSPI/ Columbia University as well as international sites, in affiliation with two NIH-funded studies, (1) SSTAR, a study of AYA social transitions and determinants (R01HD091003; PI Santelli), which will provide secondary data from the Rakai Community Cohort Study (RCCS), and (2) SUUBI4Her (R01MH113486; PI Ssewamala), an HIV prevention study for AYA girls in Uganda that will provide secondary data on mental health. Research findings and skills obtained during the K01 will position Dr. Kreniske to become an independent investigator who can contribute to the efforts to end the HIV epidemic through innovative interventions tailored to at risk AYA.